This is a GENERALIZED version of the boundaries and codes used for the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program Study-Unit investigations in the conterminous United States, excluding the High Plains Regional Ground-Water Study. The data set represents the areas to be studied during the second decade of the NAWQA Program, from 2001-2012 ("cycle 2"). The coverage is intended only for drawing ILLUSTRATIONS, NOT for spatial analysis.
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USGS Unnumbered Series
Generalized boundaries of the National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 2001-2012